It is common practice to provide for the grounding of electrical appliances so that in the event of a circuit malfunction, for example, the exposed metallic portions of the appliance cannot reach a dangerous voltage. Consequently, many, if not most, electrical receptacles include a grounding contact through which the exposed metallic portions of the appliance can be connected to the system ground. Generally, this system ground is at the potential of the standard outlet box in which the receptacle or other wiring device is mounted. Since the grounding contact is usually electrically connected to or actually part of the mounting strap, such receptacles include some means for electrically connecting the mounting strap to the outlet box. The present invention provides an advantageous way of making this connection. For convenience, we refer to wiring devices, or receptacles in t his description. The invention is not limited to receptacles, but can be used on any wiring device having a mounting strap.
U.S. Pat. No. 3,432,793 (Muska) discloses various types of metallic clips capable of exerting a yieldable pressure on the shank of the screw used to fasten the wiring device to the outlet box. The Muska device is relatively simple and inexpensive, and provides the desired low resistance connection between the mounting strap and outlet box. However, the present invention is an improvement over the device illustrated and described in the Muska patent in that it is of even simpler construction, and thus easier to manufacture, and capable of providing a more secure contact with the screw shank. Hence, a superior connection can be made with this invention. Moreover, because of the relative simplicity of the present invention, assembly of the devices of the present invention are more easily adapted to automated manufacturing than devices illustrated in the Muska patent.
The invention can be implemented at very low cost. Wiring devices, such as receptacles are sold to consumers for very low prices, often under $0.50 and, therefore, the cost of manufacture is critical. Even a fraction of a cent reduction in cost can greatly affect market share.